1. Field of the Invention
The invention relates in general to the field of communication technologies, and more particularly to a cell search method and device.
2. Description of the Related Art
The time division-synchronous code division multiple access (TD-SCDMA) system defines that one sub-frame has a total length of 6400 chips and a period of 5 ms. Each sub-frame is divided into 7 regular timeslots (Ts) and 3 special timeslots. The 7 regular timeslots are Ts0˜Ts6, each having a length of 96 chips and a period of 675 μs. The 3 special timeslots include a Down Pilot Timeslot (DwPTS) having a length of 96 chips and a period of 75 μs, a Guard Period (GP) having a length of 96 chips and a period of 75 μs, and an Up Pilot Timeslot (UpPTS) having a length of 160 chips and a period of 125 μs.
The timeslot Ts0 and the 3 following down pilot timeslots DwPTS are used for TD-SCDMA system cell search synchronization. More specifically, the timeslot Ts0 serves for down timeslots to transmit system broadcasting information, and DwPTS is used for down pilot and down synchronization.
In the TD-SCDMA cell search, in a synchronization process, Ts0 and DwPTS are detected, and cell search synchronization information therein is retrieved for the synchronization. FIG. 1 shows a schematic diagram of a TD-SCDMA cell synchronization window in the prior art. In the prior art, a first synchronization window is disposed to ensure that the search window at least includes two consecutive Ts0 and DwPTS. Thus, it is ensured that one complete set of and consecutive Ts0 and DwPTS can be found from any search starting point, so as to satisfy a common algorithm in order to perform a next synchronization process. Therefore, the first synchronization search window at least has a length of a sum of the length of one sub-frame, the length of Ts0 and the length of DwPTS (6400+864+96=7360 chips), and a period of 5.75 ms.
However, under certain circumstances, it cannot be ensured that the length of an actual synchronization window satisfies the minimum length of the first synchronization search window, resulting in a cell search synchronization failure. For example, when a TD-SCDMA/GMS dual-mode terminal is in a GSM PTM mode, the length reserved for a TD-SCDMA actual search window may be as short as 9 GSM timeslots (5.19 ms), which further includes the conversion and stabilization time reserved for GSM/TD-SCDMA RF components. In the above situation, it cannot be ensured that the actual synchronization search window meets the minimum length of 5.75 ms, meaning that the search window may not contain successive TS0 and DwPTS. As a result, the failure rate of TD-SCDMA cell search synchronization is significantly increased to degrade the transmission quality.